Nonmetallic Modified Atomically Precise Octagold Nanoclusters for Electrocatalytic Nitrate Reduction to Ammonia

Atomically precise metal nanoclusters (NCs) with metal cores functionalized by nonmetallic elements hold great promise for electrocatalytic NO₃^- reduction reaction (NO₃RR). However, elucidating structural evolution during catalysis and precisely identifying the active sites remain formidable challenges. Herein, we have synthesized [Au₈S₂(dppm)₄]²⁺ and [Au₈Se₂(dppm)₄]²⁺ (dppm: Ph₂PCH₂PPh₂) NCs with Au cores modified by S or Se atoms and subjected them to electrochemical pre-activation. Comprehensive experiments reveal that pre-activation leads to the removal of one dppm ligand from both NCs, thereby exposing metallic Au sites. As NO₃RR catalysts, the activated [Au₈S₂(dppm)₄]²⁺ achieves an NH₃ yield rate of 1108.47 mg h^-1 mg_Au^-1 and a Faradaic efficiency of 98.34%, significantly surpassing [Au₈Se₂(dppm)₄]²⁺, most reported NCs, and conventional nanocatalysts. Mechanistic studies unveil that the exposed metallic Au sites after pre-activation serve as the primary catalytic center. Furthermore, the introduction of S atoms into the Au core induces a more positive surface potential, upshifts the Au-d band center, enhances NO₃^- adsorption, and strengthens the balance between the generation and consumption of active hydrogen, collectively boosting the NO₃RR performance. This work not only provides definitive experimental evidence for structural evolution and active-site identification in atomically precise NCs under electrolysis, but also reveals the distinct effects of different nonmetallic element modifications on catalytic performance.